System and method for supporting inter-subnet control plane protocol for ensuring consistent path records in a high performance computing environment

ABSTRACT

Systems and methods for supporting consistent path records across multiple subnets in a high performance computing environment. In accordance with an embodiment, a local inter-subnet manager (ISM) can determine one or more limitations associated with a calculated local path record. The local ISM can, upon receiving information regarding path limitations from a connected subnet, determine which limitations should be applied to inter-subnet traffic.

CLAIM OF PRIORITY AND CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims the benefit of priorityto U.S. Patent Application entitled “SYSTEM AND METHOD FOR SUPPORTINGINTER-SUBNET CONTROL PLANE PROTOCOL FOR ENSURING CONSISTENT PATH RECORDSIN A HIGH PERFORMANCE COMPUTING ENVIRONMENT” application Ser. No.15/415,517, filed on Jan. 25, 2017, which application claims the benefitof priority to U.S. Provisional Patent Application entitled “SYSTEM ANDMETHOD FOR SUPPORTING ROUTER FEATURES IN A COMPUTING ENVIRONMENT”,Application No. 62/303,646, filed on Mar. 4, 2016, each of which isincorporated by reference in their entirety.

This application is related to, and incorporates by reference in itsentirety, U.S. Patent Application entitled “SYSTEM AND METHOD FORSUPPORTING ROUTER SMA ABSTRACTIONS FOR SMP CONNECTIVITY CHECKS ACROSSVIRTUAL ROUTER PORTS IN A HIGH PERFORMANCE COMPUTING ENVIRONMENT”,application Ser. No. 15/413,149, filed on Jan. 23, 2017.

COPYRIGHT NOTICE

A portion of the disclosure of this patent document contains materialwhich is subject to copyright protection. The copyright owner has noobjection to the facsimile reproduction by anyone of the patent documentor the patent disclosure, as it appears in the Patent and TrademarkOffice patent file or records, but otherwise reserves all copyrightrights whatsoever.

FIELD OF INVENTION

The present invention is generally related to computer systems, and isparticularly related to supporting inter-subnet control plane protocolfor ensuring consistent path records in a high performance computingenvironment.

BACKGROUND

As larger cloud computing architectures are introduced, the performanceand administrative bottlenecks associated with the traditional networkand storage have become a significant problem. There has been anincreased interest in using high performance lossless interconnects suchas InfiniBand (IB) technology as the foundation for a cloud computingfabric. This is the general area that embodiments of the invention areintended to address.

SUMMARY

Described herein are systems and methods for supporting an inter-subnetcontrol plane protocol for ensuring consistent path records in a highperformance computing environment, in accordance with an embodiment. Anexemplary method can provide, at one or more computers, including one ormore microprocessors, a first subnet, the first subnet comprising aplurality of switches, the plurality of switches comprising at least aleaf switch, wherein each of the plurality of switches comprise aplurality of switch ports, a plurality of end nodes, wherein theplurality of end nodes are interconnected via the plurality of switches;a subnet manager, the subnet manager running on one of the plurality ofswitches and the plurality of end nodes; and an inter-subnet manager(ISM), the inter-subnet manager running on one of the plurality ofswitches and the plurality of end nodes. The method can configure aswitch port of the plurality of switch ports as a router port. Themethod can interconnect the first subnet with a second subnet via theswitch port configured as a router port. The method can assign an endnode of the plurality of end nodes to an inter-subnet partition (ISP) ofa plurality of inter-subnet partitions. The method can calculate, by thesubnet manager, a first local path record between the switch portconfigured as a router port and the end node of the plurality of endnodes assigned to the ISP, wherein the local path record comprises atleast one limitation. The method can communicate, by the ISM, with thesecond subnet the first local path record. The method can communicate,by the ISM, with the second subnet the at least one limitation.

In accordance with an embodiment, one or more host channel adapters canbe provided (in the first or second subnet or both), and can comprise atleast one virtual function, at least one virtual switch, and at leastone physical function. The plurality of end nodes (of the first orsecond subnet) can comprise physical hosts, virtual machines, or acombination of physical hosts and virtual machines, wherein the virtualmachines are associated with at least one virtual function.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows an illustration of an InfiniBand environment, in accordancewith an embodiment.

FIG. 2 shows an illustration of a partitioned cluster environment, inaccordance with an embodiment

FIG. 3 shows an illustration of a tree topology in a networkenvironment, in accordance with an embodiment.

FIG. 4 shows an exemplary shared port architecture, in accordance withan embodiment.

FIG. 5 shows an exemplary vSwitch architecture, in accordance with anembodiment.

FIG. 6 shows an exemplary vPort architecture, in accordance with anembodiment.

FIG. 7 shows an exemplary vSwitch architecture with prepopulated LIDs,in accordance with an embodiment.

FIG. 8 shows an exemplary vSwitch architecture with dynamic LIDassignment, in accordance with an embodiment.

FIG. 9 shows an exemplary vSwitch architecture with vSwitch with dynamicLID assignment and prepopulated LIDs, in accordance with an embodiment.

FIG. 10 shows an exemplary multi-subnet InfiniBand fabric, in accordancewith an embodiment.

FIG. 11 shows an interconnection between two subnets in a highperformance computing environment, in accordance with an embodiment.

FIG. 12 shows an interconnection between two subnets via a dual-portvirtual router configuration in a high performance computingenvironment, in accordance with an embodiment.

FIG. 13 shows a flowchart of a method for supporting dual-port virtualrouter in a high performance computing environment, in accordance withan embodiment.

FIG. 14 illustrates a system for supporting unique multicast forwardingacross multiple subnets in a high performance computing environment, inaccordance with an embodiment.

FIG. 15 illustrates a system for supporting unique multicast forwardingacross multiple subnets in a high performance computing environment, inaccordance with an embodiment.

FIG. 16 illustrates a system for supporting unique multicast forwardingacross multiple subnets in a high performance computing environment, inaccordance with an embodiment.

FIG. 17 illustrates a system for supporting unique multicast forwardingacross multiple subnets in a high performance computing environment, inaccordance with an embodiment.

FIG. 18 is a flow chart of a method for supporting unique multicastforwarding across multiple subnets in a high performance computingenvironment, in accordance with an embodiment.

FIG. 19 illustrates a system for supporting an inter-subnet controlplane protocol for ensuring consistent path records, in accordance withan embodiment.

FIG. 20 illustrates a system for supporting an inter-subnet controlplane protocol for ensuring consistent path records, in accordance withan embodiment.

FIG. 21 is a flow chart of a method for supporting consistent pathrecords in a high performance computing environment, in accordance withan embodiment.

DETAILED DESCRIPTION

The invention is illustrated, by way of example and not by way oflimitation, in the figures of the accompanying drawings in which likereferences indicate similar elements. It should be noted that referencesto “an” or “one” or “some” embodiment(s) in this disclosure are notnecessarily to the same embodiment, and such references mean at leastone. While specific implementations are discussed, it is understood thatthe specific implementations are provided for illustrative purposesonly. A person skilled in the relevant art will recognize that othercomponents and configurations may be used without departing from thescope and spirit of the invention.

Common reference numerals can be used to indicate like elementsthroughout the drawings and detailed description; therefore, referencenumerals used in a figure may or may not be referenced in the detaileddescription specific to such figure if the element is describedelsewhere.

Described herein are systems and methods for supporting an inter-subnetcontrol plane protocol for ensuring consistent path records in a highperformance computing environment, in accordance with an embodiment.

The following description of the invention uses an InfiniBand™ (IB)network as an example for a high performance network. Throughout thefollowing description, reference can be made to the InfiniBand™specification (also referred to variously as the InfiniBandspecification, IB specification, or the legacy IB specification). Suchreference is understood to refer to the InfiniBand® Trade AssociationArchitecture Specification, Volume 1, Version 1.3, released March, 2015,available at http://www.inifinibandta.org, which is herein incorporatedby reference in its entirety. It will be apparent to those skilled inthe art that other types of high performance networks can be usedwithout limitation. The following description also uses the fat-treetopology as an example for a fabric topology. It will be apparent tothose skilled in the art that other types of fabric topologies can beused without limitation.

To meet the demands of the cloud in the current era (e.g., Exascaleera), it is desirable for virtual machines to be able to utilize lowoverhead network communication paradigms such as Remote Direct MemoryAccess (RDMA). RDMA bypasses the OS stack and communicates directly withthe hardware, thus, pass-through technology like Single-Root I/OVirtualization (SR-IOV) network adapters can be used. In accordance withan embodiment, a virtual switch (vSwitch) SR-IOV architecture can beprovided for applicability in high performance lossless interconnectionnetworks. As network reconfiguration time is critical to makelive-migration a practical option, in addition to network architecture,a scalable and topology-agnostic dynamic reconfiguration mechanism canbe provided.

In accordance with an embodiment, and furthermore, routing strategiesfor virtualized environments using vSwitches can be provided, and anefficient routing algorithm for network topologies (e.g., Fat-Treetopologies) can be provided. The dynamic reconfiguration mechanism canbe further tuned to minimize imposed overhead in Fat-Trees.

In accordance with an embodiment of the invention, virtualization can bebeneficial to efficient resource utilization and elastic resourceallocation in cloud computing. Live migration makes it possible tooptimize resource usage by moving virtual machines (VMs) betweenphysical servers in an application transparent manner. Thus,virtualization can enable consolidation, on-demand provisioning ofresources, and elasticity through live migration.

InfiniBand™

InfiniBand™ (IB) is an open standard lossless network technologydeveloped by the InfiniBand™ Trade Association. The technology is basedon a serial point-to-point full-duplex interconnect that offers highthroughput and low latency communication, geared particularly towardshigh-performance computing (HPC) applications and datacenters.

The InfiniBand™ Architecture (IBA) supports a two-layer topologicaldivision. At the lower layer, IB networks are referred to as subnets,where a subnet can include a set of hosts interconnected using switchesand point-to-point links. At the higher level, an IB fabric constitutesone or more subnets, which can be interconnected using routers.

Within a subnet, hosts can be connected using switches andpoint-to-point links. Additionally, there can be a master managemententity, the subnet manager (SM), which resides on a designated device inthe subnet. The subnet manager is responsible for configuring,activating and maintaining the IB subnet. Additionally, the subnetmanager (SM) can be responsible for performing routing tablecalculations in an IB fabric. Here, for example, the routing of the IBnetwork aims at proper load balancing between all source and destinationpairs in the local subnet.

Through the subnet management interface, the subnet manager exchangescontrol packets, which are referred to as subnet management packets(SMPs), with subnet management agents (SMAs). The subnet managementagents reside on every IB subnet device. By using SMPs, the subnetmanager is able to discover the fabric, configure end nodes andswitches, and receive notifications from SMAs.

In accordance with an embodiment, intra-subnet routing in an IB networkcan be based on linear forwarding tables (LFTs) stored in the switches.The LFTs are calculated by the SM according to the routing mechanism inuse. In a subnet, Host Channel Adapter (HCA) ports on the end nodes andswitches are addressed using local identifiers (LIDs). Each entry in alinear forwarding table (LFT) consists of a destination LID (DLID) andan output port. Only one entry per LID in the table is supported. When apacket arrives at a switch, its output port is determined by looking upthe DLID in the forwarding table of the switch. The routing isdeterministic as packets take the same path in the network between agiven source-destination pair (LID pair).

Generally, all other subnet managers, excepting the master subnetmanager, act in standby mode for fault-tolerance. In a situation where amaster subnet manager fails, however, a new master subnet manager isnegotiated by the standby subnet managers. The master subnet manageralso performs periodic sweeps of the subnet to detect any topologychanges and reconfigure the network accordingly.

Furthermore, hosts and switches within a subnet can be addressed usinglocal identifiers (LIDs), and a single subnet can be limited to 49151unicast LIDs. Besides the LIDs, which are the local addresses that arevalid within a subnet, each IB device can have a 64-bit global uniqueidentifier (GUID). A GUID can be used to form a global identifier (GID),which is an IB layer three (L3) address.

The SM can calculate routing tables (i.e., the connections/routesbetween each pair of nodes within the subnet) at network initializationtime. Furthermore, the routing tables can be updated whenever thetopology changes, in order to ensure connectivity and optimalperformance. During normal operations, the SM can perform periodic lightsweeps of the network to check for topology changes. If a change isdiscovered during a light sweep or if a message (trap) signaling anetwork change is received by the SM, the SM can reconfigure the networkaccording to the discovered changes.

For example, the SM can reconfigure the network when the networktopology changes, such as when a link goes down, when a device is added,or when a link is removed. The reconfiguration steps can include thesteps performed during the network initialization. Furthermore, thereconfigurations can have a local scope that is limited to the subnets,in which the network changes occurred. Also, the segmenting of a largefabric with routers may limit the reconfiguration scope.

An example InfiniBand fabric is shown in FIG. 1, which shows anillustration of an InfiniBand environment 100, in accordance with anembodiment. In the example shown in FIG. 1, nodes A-E, 101-105, use theInfiniBand fabric, 120, to communicate, via the respective host channeladapters 111-115. In accordance with an embodiment, the various nodes,e.g., nodes A-E, 101-105, can be represented by various physicaldevices. In accordance with an embodiment, the various nodes, e.g.,nodes A-E, 101-105, can be represented by various virtual devices, suchas virtual machines.

Partitioning in InfiniBand

In accordance with an embodiment, IB networks can support partitioningas a security mechanism to provide for isolation of logical groups ofsystems sharing a network fabric. Each HCA port on a node in the fabriccan be a member of one or more partitions. Partition memberships aremanaged by a centralized partition manager, which can be part of the SM.The SM can configure partition membership information on each port as atable of 16-bit partition keys (P_Keys). The SM can also configureswitch and router ports with the partition enforcement tables containingP_Key information associated with the end-nodes that send or receivedata traffic through these ports. Additionally, in a general case,partition membership of a switch port can represent a union of allmembership indirectly associated with LIDs routed via the port in anegress (towards the link) direction.

In accordance with an embodiment, partitions are logical groups of portssuch that the members of a group can only communicate to other membersof the same logical group. At host channel adapters (HCAs) and switches,packets can be filtered using the partition membership information toenforce isolation. Packets with invalid partitioning information can bedropped as soon as the packets reaches an incoming port. In partitionedIB systems, partitions can be used to create tenant clusters. Withpartition enforcement in place, a node cannot communicate with othernodes that belong to a different tenant cluster. In this way, thesecurity of the system can be guaranteed even in the presence ofcompromised or malicious tenant nodes.

In accordance with an embodiment, for the communication between nodes,Queue Pairs (QPs) and End-to-End contexts (EECs) can be assigned to aparticular partition, except for the management Queue Pairs (QP0 andQP1). The P_Key information can then be added to every IB transportpacket sent. When a packet arrives at an HCA port or a switch, its P_Keyvalue can be validated against a table configured by the SM. If aninvalid P_Key value is found, the packet is discarded immediately. Inthis way, communication is allowed only between ports sharing apartition.

An example of IB partitions is shown in FIG. 2, which shows anillustration of a partitioned cluster environment, in accordance with anembodiment. In the example shown in FIG. 2, nodes A-E, 101-105, use theInfiniBand fabric, 120, to communicate, via the respective host channeladapters 111-115. The nodes A-E are arranged into partitions, namelypartition 1, 130, partition 2, 140, and partition 3, 150. Partition 1comprises node A 101 and node D 104. Partition 2 comprises node A 101,node B 102, and node C 103. Partition 3 comprises node C 103 and node E105. Because of the arrangement of the partitions, node D 104 and node E105 are not allowed to communicate as these nodes do not share apartition. Meanwhile, for example, node A 101 and node C 103 are allowedto communicate as these nodes are both members of partition 2, 140.

Virtual Machines in InfiniBand

During the last decade, the prospect of virtualized High PerformanceComputing (HPC) environments has improved considerably as CPU overheadhas been practically removed through hardware virtualization support;memory overhead has been significantly reduced by virtualizing theMemory Management Unit; storage overhead has been reduced by the use offast SAN storages or distributed networked file systems; and network I/Ooverhead has been reduced by the use of device passthrough techniqueslike Single Root Input/Output Virtualization (SR-IOV). It is nowpossible for clouds to accommodate virtual HPC (vHPC) clusters usinghigh performance interconnect solutions and deliver the necessaryperformance.

However, when coupled with lossless networks, such as InfiniBand (IB),certain cloud functionality, such as live migration of virtual machines(VMs), still remains an issue due to the complicated addressing androuting schemes used in these solutions. IB is an interconnectionnetwork technology offering high bandwidth and low latency, thus, isvery well suited for HPC and other communication intensive workloads.

The traditional approach for connecting IB devices to VMs is byutilizing SR-IOV with direct assignment. However, achieving livemigration of VMs assigned with IB Host Channel Adapters (HCAs) usingSR-IOV has proved to be challenging. Each IB connected node has threedifferent addresses: LID, GUID, and GID. When a live migration happens,one or more of these addresses change. Other nodes communicating withthe VM-in-migration can lose connectivity. When this happens, the lostconnection can be attempted to be renewed by locating the virtualmachine's new address to reconnect to by sending Subnet Administration(SA) path record queries to the IB Subnet Manager (SM).

IB uses three different types of addresses. A first type of address isthe 16 bits Local Identifier (LID). At least one unique LID is assignedto each HCA port and each switch by the SM. The LIDs are used to routetraffic within a subnet. Since the LID is 16 bits long, 65536 uniqueaddress combinations can be made, of which only 49151 (0x0001-0xBFFF)can be used as unicast addresses. Consequently, the number of availableunicast addresses defines the maximum size of an IB subnet. A secondtype of address is the 64 bits Global Unique Identifier (GUID) assignedby the manufacturer to each device (e.g. HCAs and switches) and each HCAport. The SM may assign additional subnet unique GUIDs to an HCA port,which is useful when SR-IOV is used. A third type of address is the 128bits Global Identifier (GID). The GID is a valid IPv6 unicast address,and at least one is assigned to each HCA port. The GID is formed bycombining a globally unique 64 bits prefix assigned by the fabricadministrator, and the GUID address of each HCA port.

Fat-Tree (FTree) Topologies and Routing

In accordance with an embodiment, some of the IB based HPC systemsemploy a fat-tree topology to take advantage of the useful propertiesfat-trees offer. These properties include full bisection-bandwidth andinherent fault-tolerance due to the availability of multiple pathsbetween each source destination pair. The initial idea behind fat-treeswas to employ fatter links between nodes, with more available bandwidth,as the tree moves towards the roots of the topology. The fatter linkscan help to avoid congestion in the upper-level switches and thebisection-bandwidth is maintained.

FIG. 3 shows an illustration of a tree topology in a networkenvironment, in accordance with an embodiment. As shown in FIG. 3, oneor more end nodes 201-204 can be connected in a network fabric 200. Thenetwork fabric 200 can be based on a fat-tree topology, which includes aplurality of leaf switches 211-214, and multiple spine switches or rootswitches 231-234. Additionally, the network fabric 200 can include oneor more intermediate switches, such as switches 221-224.

Also as shown in FIG. 3, each of the end nodes 201-204 can be amulti-homed node, i.e., a single node that is connected to two or moreparts of the network fabric 200 through multiple ports. For example, thenode 201 can include the ports H1 and H2, the node 202 can include theports H3 and H4, the node 203 can include the ports H5 and H6, and thenode 204 can include the ports H7 and H8.

Additionally, each switch can have multiple switch ports. For example,the root switch 231 can have the switch ports 1-2, the root switch 232can have the switch ports 3-4, the root switch 233 can have the switchports 5-6, and the root switch 234 can have the switch ports 7-8.

In accordance with an embodiment, the fat-tree routing mechanism is oneof the most popular routing algorithm for IB based fat-tree topologies.The fat-tree routing mechanism is also implemented in the OFED (OpenFabric Enterprise Distribution—a standard software stack for buildingand deploying IB based applications) subnet manager, OpenSM.

The fat-tree routing mechanism aims to generate LFTs that evenly spreadshortest-path routes across the links in the network fabric. Themechanism traverses the fabric in the indexing order and assigns targetLIDs of the end nodes, and thus the corresponding routes, to each switchport. For the end nodes connected to the same leaf switch, the indexingorder can depend on the switch port to which the end node is connected(i.e., port numbering sequence). For each port, the mechanism canmaintain a port usage counter, and can use this port usage counter toselect a least-used port each time a new route is added.

In accordance with an embodiment, in a partitioned subnet, nodes thatare not members of a common partition are not allowed to communicate.Practically, this means that some of the routes assigned by the fat-treerouting algorithm are not used for the user traffic. The problem ariseswhen the fat tree routing mechanism generates LFTs for those routes thesame way it does for the other functional paths. This behavior canresult in degraded balancing on the links, as nodes are routed in theorder of indexing. As routing can be performed oblivious to thepartitions, fat-tree routed subnets, in general, provide poor isolationamong partitions.

In accordance with an embodiment, a Fat-Tree is a hierarchical networktopology that can scale with the available network resources. Moreover,Fat-Trees are easy to build using commodity switches placed on differentlevels of the hierarchy. Different variations of Fat-Trees are commonlyavailable, including k-ary-n-trees, Extended Generalized Fat-Trees(XGFTs), Parallel Ports Generalized Fat-Trees (PGFTs) and Real LifeFat-Trees (RLFTs).

A k-ary-n-tree is an n level Fat-Tree with k^(n) end nodes and n·k^(n−1)switches, each with 2k ports. Each switch has an equal number of up anddown connections in the tree. XGFT Fat-Tree extends k-ary-n-trees byallowing both different number of up and down connections for theswitches, and different number of connections at each level in the tree.The PGFT definition further broadens the XGFT topologies and permitsmultiple connections between switches. A large variety of topologies canbe defined using XGFTs and PGFTs. However, for practical purposes, RLFT,which is a restricted version of PGFT, is introduced to define Fat-Treescommonly found in today's HPC clusters. An RLFT uses the same port-countswitches at all levels in the Fat-Tree.

Input/Output (I/O) virtualization

In accordance with an embodiment, I/O Virtualization (IOV) can provideavailability of I/O by allowing virtual machines (VMs) to access theunderlying physical resources. The combination of storage traffic andinter-server communication impose an increased load that may overwhelmthe I/O resources of a single server, leading to backlogs and idleprocessors as they are waiting for data. With the increase in number ofI/O requests, IOV can provide availability; and can improve performance,scalability and flexibility of the (virtualized) I/O resources to matchthe level of performance seen in modern CPU virtualization.

In accordance with an embodiment, IOV is desired as it can allow sharingof I/O resources and provide protected access to the resources from theVMs. IOV decouples a logical device, which is exposed to a VM, from itsphysical implementation. Currently, there can be different types of IOVtechnologies, such as emulation, paravirtualization, direct assignment(DA), and single root-I/O virtualization (SR-IOV).

In accordance with an embodiment, one type of IOV technology is softwareemulation. Software emulation can allow for a decoupledfront-end/back-end software architecture. The front-end can be a devicedriver placed in the VM, communicating with the back-end implemented bya hypervisor to provide I/O access. The physical device sharing ratio ishigh and live migrations of VMs are possible with just a fewmilliseconds of network downtime. However, software emulation introducesadditional, undesired computational overhead.

In accordance with an embodiment, another type of IOV technology isdirect device assignment. Direct device assignment involves a couplingof I/O devices to VMs, with no device sharing between VMs. Directassignment, or device passthrough, provides near to native performancewith minimum overhead. The physical device bypasses the hypervisor andis directly attached to the VM. However, a downside of such directdevice assignment is limited scalability, as there is no sharing amongvirtual machines—one physical network card is coupled with one VM.

In accordance with an embodiment, Single Root IOV (SR-IOV) can allow aphysical device to appear through hardware virtualization as multipleindependent lightweight instances of the same device. These instancescan be assigned to VMs as passthrough devices, and accessed as VirtualFunctions (VFs). The hypervisor accesses the device through a unique(per device), fully featured Physical Function (PF). SR-IOV eases thescalability issue of pure direct assignment. However, a problempresented by SR-IOV is that it can impair VM migration. Among these IOVtechnologies, SR-IOV can extend the PCI Express (PCIe) specificationwith the means to allow direct access to a single physical device frommultiple VMs while maintaining near to native performance. Thus, SR-IOVcan provide good performance and scalability.

SR-IOV allows a PCIe device to expose multiple virtual devices that canbe shared between multiple guests by allocating one virtual device toeach guest. Each SR-IOV device has at least one physical function (PF)and one or more associated virtual functions (VF). A PF is a normal PCIefunction controlled by the virtual machine monitor (VMM), or hypervisor,whereas a VF is a light-weight PCIe function. Each VF has its own baseaddress (BAR) and is assigned with a unique requester ID that enablesI/O memory management unit (IOMMU) to differentiate between the trafficstreams to/from different VFs. The IOMMU also apply memory and interrupttranslations between the PF and the VFs.

Unfortunately, however, direct device assignment techniques pose abarrier for cloud providers in situations where transparent livemigration of virtual machines is desired for data center optimization.The essence of live migration is that the memory contents of a VM arecopied to a remote hypervisor. Then the VM is paused at the sourcehypervisor, and the VM's operation is resumed at the destination. Whenusing software emulation methods, the network interfaces are virtual sotheir internal states are stored into the memory and get copied as well.Thus the downtime could be brought down to a few milliseconds.

However, migration becomes more difficult when direct device assignmenttechniques, such as SR-IOV, are used. In such situations, a completeinternal state of the network interface cannot be copied as it is tiedto the hardware. The SR-IOV VFs assigned to a VM are instead detached,the live migration will run, and a new VF will be attached at thedestination. In the case of InfiniBand and SR-IOV, this process canintroduce downtime in the order of seconds. Moreover, in an SR-IOVshared port model the addresses of the VM will change after themigration, causing additional overhead in the SM and a negative impacton the performance of the underlying network fabric.

InfiniBand SR-IOV Architecture—Shared Port

There can be different types of SR-IOV models, e.g. a shared port model,a virtual switch model, and a virtual port model.

FIG. 4 shows an exemplary shared port architecture, in accordance withan embodiment. As depicted in the figure, a host 300 (e.g., a hostchannel adapter) can interact with a hypervisor 310, which can assignthe various virtual functions 330, 340, 350, to a number of virtualmachines. As well, the physical function can be handled by thehypervisor 310.

In accordance with an embodiment, when using a shared port architecture,such as that depicted in FIG. 4, the host, e.g., HCA, appears as asingle port in the network with a single shared LID and shared QueuePair (QP) space between the physical function 320 and the virtualfunctions 330, 350, 350. However, each function (i.e., physical functionand virtual functions) can have their own GID.

As shown in FIG. 4, in accordance with an embodiment, different GIDs canbe assigned to the virtual functions and the physical function, and thespecial queue pairs, QP0 and QP1 (i.e., special purpose queue pairs thatare used for InfiniBand management packets), are owned by the physicalfunction. These QPs are exposed to the VFs as well, but the VFs are notallowed to use QP0 (all SMPs coming from VFs towards QP0 are discarded),and QP1 can act as a proxy of the actual QP1 owned by the PF.

In accordance with an embodiment, the shared port architecture can allowfor highly scalable data centers that are not limited by the number ofVMs (which attach to the network by being assigned to the virtualfunctions), as the LID space is only consumed by physical machines andswitches in the network.

However, a shortcoming of the shared port architecture is the inabilityto provide transparent live migration, hindering the potential forflexible VM placement. As each LID is associated with a specifichypervisor, and shared among all VMs residing on the hypervisor, amigrating VM (i.e., a virtual machine migrating to a destinationhypervisor) has to have its LID changed to the LID of the destinationhypervisor. Furthermore, as a consequence of the restricted QP0 access,a subnet manager cannot run inside a VM.

InfiniBand SR-IOV Architecture Models—Virtual Switch (vSwitch)

FIG. 5 shows an exemplary vSwitch architecture, in accordance with anembodiment. As depicted in the figure, a host 400 (e.g., a host channeladapter) can interact with a hypervisor 410, which can assign thevarious virtual functions 430, 440, 450, to a number of virtualmachines. As well, the physical function can be handled by thehypervisor 410. A virtual switch 415 can also be handled by thehypervisor 401.

In accordance with an embodiment, in a vSwitch architecture each virtualfunction 430, 440, 450 is a complete virtual Host Channel Adapter(vHCA), meaning that the VM assigned to a VF is assigned a complete setof IB addresses (e.g., GID, GUID, LID) and a dedicated QP space in thehardware. For the rest of the network and the SM, the HCA 400 looks likea switch, via the virtual switch 415, with additional nodes connected toit. The hypervisor 410 can use the PF 420, and the VMs (attached to thevirtual functions) use the VFs.

In accordance with an embodiment, a vSwitch architecture providetransparent virtualization. However, because each virtual function isassigned a unique LID, the number of available LIDs gets consumedrapidly. As well, with many LID addresses in use (i.e., one each foreach physical function and each virtual function), more communicationpaths have to be computed by the SM and more Subnet Management Packets(SMPs) have to be sent to the switches in order to update their LFTs.For example, the computation of the communication paths might takeseveral minutes in large networks. Because LID space is limited to 49151unicast LIDs, and as each VM (via a VF), physical node, and switchoccupies one LID each, the number of physical nodes and switches in thenetwork limits the number of active VMs, and vice versa.

InfiniBand SR-IOV Architecture Models—Virtual Port (vPort)

FIG. 6 shows an exemplary vPort concept, in accordance with anembodiment. As depicted in the figure, a host 300 (e.g., a host channeladapter) can interact with a hypervisor 410, which can assign thevarious virtual functions 330, 340, 350, to a number of virtualmachines. As well, the physical function can be handled by thehypervisor 310.

In accordance with an embodiment, the vPort concept is loosely definedin order to give freedom of implementation to vendors (e.g. thedefinition does not rule that the implementation has to be SRIOVspecific), and a goal of the vPort is to standardize the way VMs arehandled in subnets. With the vPort concept, both SR-IOV Shared-Port-likeand vSwitch-like architectures or a combination of both, that can bemore scalable in both the space and performance domains, can be defined.A vPort supports optional LIDs, and unlike the Shared-Port, the SM isaware of all the vPorts available in a subnet even if a vPort is notusing a dedicated LID.

InfiniBand SR-IOV Architecture Models—vSwitch with Prepopulated LIDs

In accordance with an embodiment, the present disclosure provides asystem and method for providing a vSwitch architecture with prepopulatedLIDs.

FIG. 7 shows an exemplary vSwitch architecture with prepopulated LIDs,in accordance with an embodiment. As depicted in the figure, a number ofswitches 501-504 can provide communication within the network switchedenvironment 600 (e.g., an IB subnet) between members of a fabric, suchas an InfiniBand fabric. The fabric can include a number of hardwaredevices, such as host channel adapters 510, 520, 530. Each of the hostchannel adapters 510, 520, 530, can in turn interact with a hypervisor511, 521, and 531, respectively. Each hypervisor can, in turn, inconjunction with the host channel adapter it interacts with, setup andassign a number of virtual functions 514, 515, 516, 524, 525, 526, 534,535, 536, to a number of virtual machines. For example, virtual machine1 550 can be assigned by the hypervisor 511 to virtual function 1 514.Hypervisor 511 can additionally assign virtual machine 2 551 to virtualfunction 2 515, and virtual machine 3 552 to virtual function 3 516.Hypervisor 531 can, in turn, assign virtual machine 4 553 to virtualfunction 1 534. The hypervisors can access the host channel adaptersthrough a fully featured physical function 513, 523, 533, on each of thehost channel adapters.

In accordance with an embodiment, each of the switches 501-504 cancomprise a number of ports (not shown), which are used in setting alinear forwarding table in order to direct traffic within the networkswitched environment 600.

In accordance with an embodiment, the virtual switches 512, 522, and532, can be handled by their respective hypervisors 511, 521, 531. Insuch a vSwitch architecture each virtual function is a complete virtualHost Channel Adapter (vHCA), meaning that the VM assigned to a VF isassigned a complete set of IB addresses (e.g., GID, GUID, LID) and adedicated QP space in the hardware. For the rest of the network and theSM (not shown), the HCAs 510, 520, and 530 look like a switch, via thevirtual switches, with additional nodes connected to them.

In accordance with an embodiment, the present disclosure provides asystem and method for providing a vSwitch architecture with prepopulatedLIDs. Referring to FIG. 7, the LIDs are prepopulated to the variousphysical functions 513, 523, 533, as well as the virtual functions514-516, 524-526, 534-536 (even those virtual functions not currentlyassociated with an active virtual machine). For example, physicalfunction 513 is prepopulated with LID 1, while virtual function 1 534 isprepopulated with LID 10. The LIDs are prepopulated in an SR-IOVvSwitch-enabled subnet when the network is booted. Even when not all ofthe VFs are occupied by VMs in the network, the populated VFs areassigned with a LID as shown in FIG. 7.

In accordance with an embodiment, much like physical host channeladapters can have more than one port (two ports are common forredundancy), virtual HCAs can also be represented with two ports and beconnected via one, two or more virtual switches to the external IBsubnet.

In accordance with an embodiment, in a vSwitch architecture withprepopulated LIDs, each hypervisor can consume one LID for itselfthrough the PF and one more LID for each additional VF. The sum of allthe VFs available in all hypervisors in an IB subnet, gives the maximumamount of VMs that are allowed to run in the subnet. For example, in anIB subnet with 16 virtual functions per hypervisor in the subnet, theneach hypervisor consumes 17 LIDs (one LID for each of the 16 virtualfunctions plus one LID for the physical function) in the subnet. In suchan IB subnet, the theoretical hypervisor limit for a single subnet isruled by the number of available unicast LIDs and is: 2891 (49151available LIDs divided by 17 LIDs per hypervisor), and the total numberof VMs (i.e., the limit) is 46256 (2891 hypervisors times 16 VFs perhypervisor). (In actuality, these numbers are actually smaller sinceeach switch, router, or dedicated SM node in the IB subnet consumes aLID as well). Note that the vSwitch does not need to occupy anadditional LID as it can share the LID with the PF

In accordance with an embodiment, in a vSwitch architecture withprepopulated LIDs, communication paths are computed for all the LIDs thefirst time the network is booted. When a new VM needs to be started thesystem does not have to add a new LID in the subnet, an action thatwould otherwise cause a complete reconfiguration of the network,including path recalculation, which is the most time consuming part.Instead, an available port for a VM is located (i.e., an availablevirtual function) in one of the hypervisors and the virtual machine isattached to the available virtual function.

In accordance with an embodiment, a vSwitch architecture withprepopulated LIDs also allows for the ability to calculate and usedifferent paths to reach different VMs hosted by the same hypervisor.Essentially, this allows for such subnets and networks to use a LID MaskControl (LMC) like feature to provide alternative paths towards onephysical machine, without being bound by the limitation of the LMC thatrequires the LIDs to be sequential. The freedom to use non-sequentialLIDs is particularly useful when a VM needs to be migrated and carry itsassociated LID to the destination.

In accordance with an embodiment, along with the benefits shown above ofa vSwitch architecture with prepopulated LIDs, certain considerationscan be taken into account. For example, because the LIDs areprepopulated in an SR-IOV vSwitch-enabled subnet when the network isbooted, the initial path computation (e.g., on boot-up) can take longerthan if the LIDs were not pre-populated.

InfiniBand SR-IOV Architecture Models—vSwitch with Dynamic LIDAssignment

In accordance with an embodiment, the present disclosure provides asystem and method for providing a vSwitch architecture with dynamic LIDassignment.

FIG. 8 shows an exemplary vSwitch architecture with dynamic LIDassignment, in accordance with an embodiment. As depicted in the figure,a number of switches 501-504 can provide communication within thenetwork switched environment 700 (e.g., an IB subnet) between members ofa fabric, such as an InfiniBand fabric. The fabric can include a numberof hardware devices, such as host channel adapters 510, 520, 530. Eachof the host channel adapters 510, 520, 530, can in turn interact with ahypervisor 511, 521, 531, respectively. Each hypervisor can, in turn, inconjunction with the host channel adapter it interacts with, setup andassign a number of virtual functions 514, 515, 516, 524, 525, 526, 534,535, 536, to a number of virtual machines. For example, virtual machine1 550 can be assigned by the hypervisor 511 to virtual function 1 514.Hypervisor 511 can additionally assign virtual machine 2 551 to virtualfunction 2 515, and virtual machine 3 552 to virtual function 3 516.Hypervisor 531 can, in turn, assign virtual machine 4 553 to virtualfunction 1 534. The hypervisors can access the host channel adaptersthrough a fully featured physical function 513, 523, 533, on each of thehost channel adapters.

In accordance with an embodiment, each of the switches 501-504 cancomprise a number of ports (not shown), which are used in setting alinear forwarding table in order to direct traffic within the networkswitched environment 700.

In accordance with an embodiment, the virtual switches 512, 522, and532, can be handled by their respective hypervisors 511, 521, 531. Insuch a vSwitch architecture each virtual function is a complete virtualHost Channel Adapter (vHCA), meaning that the VM assigned to a VF isassigned a complete set of IB addresses (e.g., GID, GUID, LID) and adedicated QP space in the hardware. For the rest of the network and theSM (not shown), the HCAs 510, 520, and 530 look like a switch, via thevirtual switches, with additional nodes connected to them.

In accordance with an embodiment, the present disclosure provides asystem and method for providing a vSwitch architecture with dynamic LIDassignment. Referring to FIG. 8, the LIDs are dynamically assigned tothe various physical functions 513, 523, 533, with physical function 513receiving LID 1, physical function 523 receiving LID 2, and physicalfunction 533 receiving LID 3. Those virtual functions that areassociated with an active virtual machine can also receive a dynamicallyassigned LID. For example, because virtual machine 1 550 is active andassociated with virtual function 1 514, virtual function 514 can beassigned LID 5. Likewise, virtual function 2 515, virtual function 3516, and virtual function 1 534 are each associated with an activevirtual function. Because of this, these virtual functions are assignedLIDs, with LID 7 being assigned to virtual function 2 515, LID 11 beingassigned to virtual function 3 516, and LID 9 being assigned to virtualfunction 1 534. Unlike vSwitch with prepopulated LIDs, those virtualfunctions not currently associated with an active virtual machine do notreceive a LID assignment.

In accordance with an embodiment, with the dynamic LID assignment, theinitial path computation can be substantially reduced. When the networkis booting for the first time and no VMs are present then a relativelysmall number of LIDs can be used for the initial path calculation andLFT distribution.

In accordance with an embodiment, much like physical host channeladapters can have more than one port (two ports are common forredundancy), virtual HCAs can also be represented with two ports and beconnected via one, two or more virtual switches to the external IBsubnet.

In accordance with an embodiment, when a new VM is created in a systemutilizing vSwitch with dynamic LID assignment, a free VM slot is foundin order to decide on which hypervisor to boot the newly added VM, and aunique non-used unicast LID is found as well. However, there are noknown paths in the network and the LFTs of the switches for handling thenewly added LID. Computing a new set of paths in order to handle thenewly added VM is not desirable in a dynamic environment where severalVMs may be booted every minute. In large IB subnets, computing a new setof routes can take several minutes, and this procedure would have torepeat each time a new VM is booted.

Advantageously, in accordance with an embodiment, because all the VFs ina hypervisor share the same uplink with the PF, there is no need tocompute a new set of routes. It is only needed to iterate through theLFTs of all the physical switches in the network, copy the forwardingport from the LID entry that belongs to the PF of the hypervisor—wherethe VM is created—to the newly added LID, and send a single SMP toupdate the corresponding LFT block of the particular switch. Thus thesystem and method avoids the need to compute a new set of routes.

In accordance with an embodiment, the LIDs assigned in the vSwitch withdynamic LID assignment architecture do not have to be sequential. Whencomparing the LIDs assigned on VMs on each hypervisor in vSwitch withprepopulated LIDs versus vSwitch with dynamic LID assignment, it isnotable that the LIDs assigned in the dynamic LID assignmentarchitecture are non-sequential, while those prepopulated in aresequential in nature. In the vSwitch dynamic LID assignmentarchitecture, when a new VM is created, the next available LID is usedthroughout the lifetime of the VM. Conversely, in a vSwitch withprepopulated LIDs, each VM inherits the LID that is already assigned tothe corresponding VF, and in a network without live migrations, VMsconsecutively attached to a given VF get the same LID.

In accordance with an embodiment, the vSwitch with dynamic LIDassignment architecture can resolve the drawbacks of the vSwitch withprepopulated LIDs architecture model at a cost of some additionalnetwork and runtime SM overhead. Each time a VM is created, the LFTs ofthe physical switches in the subnet are updated with the newly added LIDassociated with the created VM. One subnet management packet (SMP) perswitch is needed to be sent for this operation. The LMC-likefunctionality is also not available, because each VM is using the samepath as its host hypervisor. However, there is no limitation on thetotal amount of VFs present in all hypervisors, and the number of VFsmay exceed that of the unicast LID limit. Of course, not all of the VFsare allowed to be attached on active VMs simultaneously if this is thecase, but having more spare hypervisors and VFs adds flexibility fordisaster recovery and optimization of fragmented networks when operatingclose to the unicast LID limit.

InfiniBand SR-IOV Architecture Models—vSwitch with Dynamic LIDAssignment and Prepopulated LIDs

FIG. 9 shows an exemplary vSwitch architecture with vSwitch with dynamicLID assignment and prepopulated LIDs, in accordance with an embodiment.As depicted in the figure, a number of switches 501-504 can providecommunication within the network switched environment 800 (e.g., an IBsubnet) between members of a fabric, such as an InfiniBand fabric. Thefabric can include a number of hardware devices, such as host channeladapters 510, 520, 530. Each of the host channel adapters 510, 520, 530,can in turn interact with a hypervisor 511, 521, and 531, respectively.Each hypervisor can, in turn, in conjunction with the host channeladapter it interacts with, setup and assign a number of virtualfunctions 514, 515, 516, 524, 525, 526, 534, 535, 536, to a number ofvirtual machines. For example, virtual machine 1 550 can be assigned bythe hypervisor 511 to virtual function 1 514. Hypervisor 511 canadditionally assign virtual machine 2 551 to virtual function 2 515.Hypervisor 521 can assign virtual machine 3 552 to virtual function 3526. Hypervisor 531 can, in turn, assign virtual machine 4 553 tovirtual function 2 535. The hypervisors can access the host channeladapters through a fully featured physical function 513, 523, 533, oneach of the host channel adapters.

In accordance with an embodiment, each of the switches 501-504 cancomprise a number of ports (not shown), which are used in setting alinear forwarding table in order to direct traffic within the networkswitched environment 800.

In accordance with an embodiment, the virtual switches 512, 522, and532, can be handled by their respective hypervisors 511, 521, 531. Insuch a vSwitch architecture each virtual function is a complete virtualHost Channel Adapter (vHCA), meaning that the VM assigned to a VF isassigned a complete set of IB addresses (e.g., GID, GUID, LID) and adedicated QP space in the hardware. For the rest of the network and theSM (not shown), the HCAs 510, 520, and 530 look like a switch, via thevirtual switches, with additional nodes connected to them.

In accordance with an embodiment, the present disclosure provides asystem and method for providing a hybrid vSwitch architecture withdynamic LID assignment and prepopulated LIDs. Referring to FIG. 9,hypervisor 511 can be arranged with vSwitch with prepopulated LIDsarchitecture, while hypervisor 521 can be arranged with vSwitch withprepopulated LIDs and dynamic LID assignment. Hypervisor 531 can bearranged with vSwitch with dynamic LID assignment. Thus, the physicalfunction 513 and virtual functions 514-516 have their LIDs prepopulated(i.e., even those virtual functions not attached to an active virtualmachine are assigned a LID). Physical function 523 and virtual function1 524 can have their LIDs prepopulated, while virtual function 2 and 3,525 and 526, have their LIDs dynamically assigned (i.e., virtualfunction 2 525 is available for dynamic LID assignment, and virtualfunction 3 526 has a LID of 11 dynamically assigned as virtual machine 3552 is attached). Finally, the functions (physical function and virtualfunctions) associated with hypervisor 3 531 can have their LIDsdynamically assigned. This results in virtual functions 1 and 3, 534 and536, are available for dynamic LID assignment, while virtual function 2535 has LID of 9 dynamically assigned as virtual machine 4 553 isattached there.

In accordance with an embodiment, such as that depicted in FIG. 9, whereboth vSwitch with prepopulated LIDs and vSwitch with dynamic LIDassignment are utilized (independently or in combination within anygiven hypervisor), the number of prepopulated LIDs per host channeladapter can be defined by a fabric administrator and can be in the rangeof 0<=prepopulated VFs<=Total VFs (per host channel adapter), and theVFs available for dynamic LID assignment can be found by subtracting thenumber of prepopulated VFs from the total number of VFs (per hostchannel adapter).

In accordance with an embodiment, much like physical host channeladapters can have more than one port (two ports are common forredundancy), virtual HCAs can also be represented with two ports and beconnected via one, two or more virtual switches to the external IBsubnet.

InfiniBand—Inter-Subnet Communication (Fabric Manager)

In accordance with an embodiment, in addition to providing an InfiniBandfabric within a single subnet, embodiments of the current disclosure canalso provide for an InfiniBand fabric that spans two or more subnets.

FIG. 10 shows an exemplary multi-subnet InfiniBand fabric, in accordancewith an embodiment. As depicted in the figure, within subnet A 1000, anumber of switches 1001-1004 can provide communication within subnet A1000 (e.g., an IB subnet) between members of a fabric, such as anInfiniBand fabric. The fabric can include a number of hardware devices,such as, for example, channel adapter 1010. Host channel adapter 1010can in turn interact with a hypervisor 1011. The hypervisor can, inturn, in conjunction with the host channel adapter it interacts with,setup a number of virtual functions 1014. The hypervisor canadditionally assign virtual machines to each of the virtual functions,such as virtual machine 1 1015 being assigned to virtual function 11014. The hypervisor can access their associated host channel adaptersthrough a fully featured physical function, such as physical function1013, on each of the host channel adapters. Within subnet B 1040, anumber of switches 1021-1024 can provide communication within subnet B1040 (e.g., an IB subnet) between members of a fabric, such as anInfiniBand fabric. The fabric can include a number of hardware devices,such as, for example, channel adapter 1030. Host channel adapter 1030can in turn interact with a hypervisor 1031. The hypervisor can, inturn, in conjunction with the host channel adapter it interacts with,setup a number of virtual functions 1034. The hypervisor canadditionally assign virtual machines to each of the virtual functions,such as virtual machine 2 1035 being assigned to virtual function 21034. The hypervisor can access their associated host channel adaptersthrough a fully featured physical function, such as physical function1033, on each of the host channel adapters. It is noted that althoughonly one host channel adapter is shown within each subnet (i.e., subnetA and subnet B), it is to be understood that a plurality of host channeladapters, and their corresponding components, can be included withineach subnet.

In accordance with an embodiment, each of the host channel adapters canadditionally be associated with a virtual switch, such as virtual switch1012 and virtual switch 1032, and each HCA can be set up with adifferent architecture model, as discussed above. Although both subnetswithin FIG. 10 are shown as using a vSwitch with prepopulated LIDarchitecture model, this is not meant to imply that all such subnetconfigurations must follow a similar architecture model.

In accordance with an embodiment, at least one switch within each subnetcan be associated with a router, such as switch 1002 within subnet A1000 being associated with router 1005, and switch 1021 within subnet B1040 being associated with router 1006.

In accordance with an embodiment, at least one device (e.g., a switch, anode . . . etc.) can be associated with a fabric manager (not shown).The fabric manager can be used, for example, to discover inter-subnetfabric topology, create a fabric profile (e.g., a virtual machine fabricprofile), build virtual machine related database objects that forms thebasis for building a virtual machine fabric profile. In addition, thefabric manager can define legal inter-subnet connectivity in terms ofwhich subnets are allowed to communicate via which router ports usingwhich partition numbers.

In accordance with an embodiment, when traffic at an originating source,such as virtual machine 1 within subnet A, is addressed to a destinationin a different subnet, such as virtual machine 2 within subnet B, thetraffic can be addressed to the router within subnet A, i.e., router1005, which can then pass the traffic to subnet B via its link withrouter 1006.

Virtual Dual Port Router

In accordance with an embodiment, a dual port router abstraction canprovide a simple way for enabling subnet-to-subnet router functionalityto be defined based on a switch hardware implementation that has theability to do GRH (global route header) to LRH (local route header)conversion in addition to performing normal LRH based switching.

In accordance with an embodiment, a virtual dual-port router canlogically be connected outside a corresponding switch port. This virtualdual-port router can provide an InfiniBand specification compliant viewto a standard management entity, such as a Subnet Manager.

In accordance with an embodiment, a dual-ported router model impliesthat different subnets can be connected in a way where each subnet fullycontrols the forwarding of packets as well as address mappings in theingress path to the subnet, and without impacting the routing andlogical connectivity within either of the incorrectly connected subnets.

In accordance with an embodiment, in a situation involving anincorrectly connected fabric, the use of a virtual dual-port routerabstraction can also allow a management entity, such as a Subnet Managerand IB diagnostic software, to behave correctly in the presence ofun-intended physical connectivity to a remote subnet.

FIG. 11 shows an interconnection between two subnets in a highperformance computing environment, in accordance with an embodiment.Prior to configuration with a virtual dual port router, a switch 1120 insubnet A 1101 can be connected through a switch port 1121 of switch1120, via a physical connection 1110, to a switch 1130 in subnet B 1102,via a switch port 1131 of switch 1130. In such an embodiment, eachswitch port, 1121 and 1131, can act both as switch ports and routerports.

In accordance with an embodiment, a problem with this configuration isthat a management entity, such as a subnet manager in an InfiniBandsubnet, cannot distinguish between a physical port that is both a switchport and a router port. In such a situation, a SM can treat the switchport as having a router port connected to that switch port. But if theswitch port is connected to another subnet, via, for example, a physicallink, with another subnet manager, then the subnet manager can be ableto send a discovery message out on the physical link. However, such adiscovery message cannot be allowed at the other subnet.

FIG. 12 shows an interconnection between two subnets via a dual-portvirtual router configuration in a high performance computingenvironment, in accordance with an embodiment.

In accordance with an embodiment, after configuration, a dual-portvirtual router configuration can be provided such that a subnet managersees a proper end node, signifying an end of the subnet that the subnetmanager is responsible for.

In accordance with an embodiment, at a switch 1220 in subnetA 1201, aswitch port can be connected (i.e., logically connected) to a routerport 1211 in a virtual router 1210 via a virtual link 1223. The virtualrouter 1210 (e.g., a dual-port virtual router), which while shown asbeing external to the switch 1220 can, in embodiments, be logicallycontained within the switch 1220, can also comprise a second routerport, router port II 1212. In accordance with an embodiment, a physicallink 1203, which can have two ends, can connect the subnetA 1201 viafirst end of the physical link with subnet B 1202 via a second end ofthe physical link, via router port II 1212 and router port II 1232,contained in virtual router 1230 in subnet B 1202. Virtual router 1230can additionally comprise router port 1231, which can be connected(i.e., logically connected) to switch port 1241 on switch 1240 via avirtual link 1233.

In accordance with an embodiment, a subnet manager (not shown) onsubnetA can detect router port 1211, on virtual router 1210 as an endpoint of the subnet that the subnet manager controls. The dual-portvirtual router abstraction can allow the subnet manager on subnet A todeal with subnetA in a usual manner (e.g., as defined per theInifiniBand specification). At the subnet management agent level, thedual-port virtual router abstraction can be provided such that the SMsees the normal switch port, and then at the SMA level, the abstractionthat there is another port connected to the switch port, and this portis a router port on a dual-port virtual router. In the local SM, aconventional fabric topology can continue to be used (the SM sees theport as a standard switch port in the topology), and thus the SM seesthe router port as an end port. Physical connection can be made betweentwo switch ports that are also configured as router ports in twodifferent subnets.

In accordance with an embodiment, the dual-port virtual router can alsoresolve the issue that a physical link could be mistakenly connected tosome other switch port in the same subnet, or to a switch port that wasnot intended to provide a connection to another subnet. Therefore, themethods and systems described herein also provide a representation ofwhat is on the outside of a subnet.

In accordance with an embodiment, within a subnet, such as subnet A, alocal SM determines a switch port, and then determines a router portconnected to that switch port (e.g., router port 1211 connected, via avirtual link 1223, to switch port 1221). Because the SM sees the routerport 1211 as the end of the subnet that the SM manages, the SM cannotsend discovery and/or management messages beyond this point (e.g., torouter port II 1212).

In accordance with an embodiment, the dual-port virtual router describedabove provides a benefit that the dual-port virtual router abstractionis entirely managed by a management entity (e.g., SM or SMA) within thesubnet that the dual-port virtual router belongs to. By allowingmanagement solely on the local side, a system does not have to providean external, independent management entity. That is, each side of asubnet to subnet connection can be responsible for configuring its owndual-port virtual router.

In accordance with an embodiment, in a situation where a packet, such asan SMP, is addressed to a remote destination (i.e., outside of the localsubnet) arrives local target port that is not configured via thedual-port virtual router described above, then the local port can returna message specifying that it is not a router port.

Many features of the present invention can be performed in, using, orwith the assistance of hardware, software, firmware, or combinationsthereof. Consequently, features of the present invention may beimplemented using a processing system (e.g., including one or moreprocessors).

FIG. 13 shows a method for supporting dual-port virtual router in a highperformance computing environment, in accordance with an embodiment. Atstep 1310, the method can provide at one or more computers, includingone or more microprocessors, a first subnet, the first subnet comprisinga plurality of switches, the plurality of switches comprising at least aleaf switch, wherein each of the plurality of switches comprise aplurality of switch ports, a plurality of host channel adapters, eachhost channel adapter comprising at least one host channel adapter port,a plurality of end nodes, wherein each of the end nodes are associatedwith at least one host channel adapter of the plurality of host channeladapters, and a subnet manager, the subnet manager running on one of theplurality of switches and the plurality of host channel adapters.

At step 1320, the method can configure a switch port of the plurality ofswitch ports on a switch of the plurality of switches as a router port.

At step 1330, the method can logically connect the switch portconfigured as the router port to a virtual router, the virtual routercomprising at least two virtual router ports.

Ensuring Unique Multicast across Multiple Connected Subnets

In accordance with an embodiment, a system can support multicastrouting. Multicast routing is a one-to-many/many-to-many communicationparadigm designed to simplify and improve the efficiency ofcommunication between a set of end nodes (e.g., hosts, virtual machines. . . etc.).

In accordance with an embodiment, in a single subnet system, a multicastgroup can be identified by a unique GID. End nodes can be joined to orleave a multicast group through a management action where the nodesupplies the identity (GID) for each port that will participate. Thisinformation can be distributed to the switches. Each switch isconfigured with routing information for the multicast traffic whichspecifies all of the local switch ports where the packet is addressed totravel. Care is taken to assure there are no loops (i.e., a singlespanning tree such that a packet is not forwarded to a switch thatalready processed that packet).

In accordance with an embodiment, the node uses the multicast LID andGID in all packets it sends to that multicast group. When a switchreceives a multicast packet (i.e., a packet with a multicast LID in thepacket's DLID field) it replicates the packet and sends it out to eachof the designated ports except the arrival port. In this fashion, eachcascaded switch replicates the packet such that the packet arrives onlyonce at every subscribed end node.

In accordance with an embodiment, a channel adapter may limit the numberof QPs that can register for the same multicast address. The channeladapter distributes multicast packets to QPs registered for thatmulticast address. A single QP can be registered for multiple addressesfor the same port but if a consumer wishes to receive multicast trafficon multiple ports it needs a different QP for each port. The channeladapter recognizes a multicast packet by the packet's DLID or by thespecial value in the packet's Destination QP field and routes the packetto the QPs registered for that address and port.

In accordance with an embodiment, multicast routing withininterconnected subnets requires a global view and a single globalspanning tree in order to ensure that a single multicast packet is notdelivered more than once to each potential receiver end-point.

In accordance with an embodiment, by enforcing that incoming (i.e.,incoming on a router port of a subnet) multicast packets have SGIDs(source global identifiers) that correspond to a restricted set ofsource subnet numbers when entering the ingress router ports to a localsubnet, it is possible to ensure that multicast packets sent from onesubnet are never returned to the same subnet through a different set ofconnected router ports (i.e., avoid looping multicast packets).

In accordance with an embodiment, in a situation with two directlyconnected subnets, such loop avoidance can be achieved by enforcing thatall incoming multicast packets have the source subnet prefix thatcorresponds to the neighbor subnet. Put another way, in order to enforceloop avoidance, MC packets received at an ingress port of a routerwithin a subnet can be checked to determine if the inbound MC packetcomprises a subnet prefix that is the same as the subnet prefix of thesubnet at which the MC packet is received. If so, the packet can bedropped at the router in order to avoid a loop.

FIG. 14 illustrates a system for supporting unique multicast forwardingacross multiple subnets in a high performance computing environment, inaccordance with an embodiment.

In accordance with an embodiment, a system can comprise two or moresubnets, such as subnet A 1400 and subnet B 1410. Subnets A and B cancomprise a number of end nodes, respectively, such as end node 1401, endnode 1402, end node 1411, and end node 1412. In an effort forsimplicity, the configuration of the end nodes is not explicitly shownin the figure. One of ordinary skill in the art will understand that theend nodes can comprise a number of configurations, such as thosedescribed above in relation to physical end nodes, virtual machines,virtual switches, and the like. Subnet A can additionally comprise anumber of switches, representatively shown as switches 1404-1407, and anumber of routers, such as routers 1403 and 1408. Subnet B can likewiseadditionally comprise a number of switches, representatively shown asswitches 1414-1417, and a number of routers, such as routers 1413 and1418. It is to be understood that the routers, although shown asseparate components, can also comprise a virtual router, such as thedual-port virtual router configuration.

For example, in accordance with an embodiment, after configuration, adual-port virtual router configuration can be provided such that asubnet manager sees a proper end node, signifying an end of the subnetthat the subnet manager is responsible for. In accordance with anembodiment, at a switch 1404 in subnet A 1400, a switch port can beconnected (i.e., logically connected) to a router port in a virtualrouter 1405 via a virtual link. The virtual router 1403 (e.g., adual-port virtual router), which while shown as being external to theswitch 1404 can, in embodiments, be logically contained within theswitch 1404, can also comprise a second router port, router port II. Inaccordance with an embodiment, a physical link, which can have two ends,can connect the subnet A 1400 via first end of the physical link withsubnet B 1401 via a second end of the physical link, via router ports atthe routers in the different subnets.

In accordance with an embodiment, end node 1412 can initiate an MCpacket 1450. The MC packet 1450 can be associated with a number ofdifferent elements (not shown), such as a MCG (multicastgroup—representing a list of addresses to which the MC packet needs tobe distributed), as well as an SGID (source global identifier). TheSGID, in addition to indicating the source of the MC packet 1450,additionally comprises a source subnet identifier, identifying thesource of the MC packet as subnet B 1410.

In accordance with an embodiment, end nodes can be joined to or leave amulticast group through a management action where the node supplies theLID for each port that will participate. This information can bedistributed to the switches. Each switch is configured with routinginformation for the multicast traffic which specifies all of the portswhere the packet is addressed to travel. Care is taken to assure thereare no loops (i.e., a single spanning tree such that a packet is notforwarded to a switch that already processed that packet).

In accordance with an embodiment, the node uses the multicast LID andGID in all packets it sends to that multicast group. When a switchreceives a multicast packet (i.e., a packet with a multicast LID in thepacket's DLID field) it replicates the packet and sends it out to eachof the designated ports except the arrival port. In this fashion, eachcascaded switch replicates the packet such that the packet arrives onlyonce at every subscribed end node.

In accordance with an embodiment, each MC packet is originated from asource node/host—that source comprises a layer 3 source address, whichis unique source address, and also has a layer 3 destination addresseswhich represents the group (128 bit global id). A MC packet is a packetof a special class that comprises a global router header regardless ofwhether it is only sent within a local subnet or if it is sentinter-subnet. In accordance with an embodiment, the source addresscomprises the source subnet number of the originating node. In the caseof directly connected subnets, any packet received from a port connectedto the remote subnet can have a source address representing the SubnetID of the peer subnet.

In accordance with an embodiment, as shown in FIG. 15, which illustratesa system for supporting unique multicast forwarding across multiplesubnets in a high performance computing environment, in accordance withan embodiment, once the MC packet arrives at a switch, such as switch1417, the switch, as determined by the existing routing tables and MCGtables in memory at the switch, replicates the MC packet 1450 andaddresses it to the different locations. In the situation shown in FIG.15, the MC packet 1450 is forwarded to end node 1411, as well as acrossa link between router 1413 and router 1403, into subnet A 1400.

In accordance with an embodiment, as shown in FIG. 16, which illustratesa system for supporting unique multicast forwarding across multiplesubnets in a high performance computing environment, in accordance withan embodiment, once the MC packet arrives in subnet A 1400, the MCpacket is replicated an additional number of times. For example, switch1404 can replicate the MC packet such that the packet is addressed toend nodes 1401 and 1402. However, because the MC packet is replicatedand sent out across the paths, excluding the originating path, the MCpacket 1450 can also be addressed back to subnet B 1410 on a linkbetween router 1408 and 1418.

In accordance with an embodiment, as shown in FIG. 17, which illustratesa system for supporting unique multicast forwarding across multiplesubnets in a high performance computing environment, in accordance withan embodiment, once the MC packet arrives at an ingress port at router1418, the router 1418 can read the packet header of the MC packet 1450.Because the packet header of MC packet 1450 comprises the SGIDidentifying subnet B as the source of the MC packet, router 1418 candetermine, by, for example, comparing the source identifier of MC Packet1450 with the identity of the subnet in which router B resides, that theMC packet originated in subnet B (i.e., compare the source subnet numberof the MC packet with the subnet that the MC packet arrives at). If thedetermination reveals that the MC packet is arriving at the subnet inwhich the MC packet originated, the router can drop the MC packet so asto avoid a loop. In other words, at ingress, the router port verifiesthat the source subnet number is not the local subnet number.

FIG. 18 is a flow chart of a method for supporting unique multicastforwarding across multiple subnets in a high performance computingenvironment, in accordance with an embodiment.

At step 1810, the method can provide, at one or more computers,including one or more microprocessors, a first subnet, the first subnetcomprising a plurality of switches, the plurality of switches comprisingat least a leaf switch, wherein each of the plurality of switchescomprise a plurality of switch ports, a plurality of host channeladapters, each host channel adapter comprising at least one host channeladapter port, a plurality of end nodes, wherein the plurality of endnodes are interconnected via the plurality of switches, and a subnetmanager, the subnet manager running on one of the plurality of switchesand the plurality of end nodes.

At step 1820, the method can configure a switch port of the plurality ofswitch ports on a switch of the plurality of switches as a router port.

At step 1830, the method can configure a second switch port of theplurality of switch ports on a second switch of the plurality ofswitches as a second router port.

At step 1840, the method can interconnect the first subnet with a secondsubnet via the router port and the second router port.

At step 1850, the method can send, from an end node of the plurality ofend nodes, a multicast packet, wherein the multicast packet comprises asource global identifier (SGID).

In accordance with an embodiment, each router port can check the SGID ofmulticast packets arriving from the peer subnet via the physical link,and discard any such multicast packets that have an SGID that representsthe same Subnet ID as the local subnet.

Inter-Subnet Control Plane Protocol for Ensuring Consistent Path Records

In accordance with an embodiment, systems and methods can provide for acontrol plane protocol to ensure consistent path records betweenconnected subnets in a high performance computing environment.

In accordance with an embodiment, when an end node of a local subnet isa member of an inter-subnet partition (ISP), then it is subject forcommunication with nodes in other subnets via router ports that are alsomembers of the same ISP.

In accordance with an embodiment, certain partitions can be classifiedas “Inter Subnet Partitions” (also referred to herein as ISPs). Whensuch certain partitions are thus classified, subnet management entities(e.g., SMs or inter-subnet managers (ISMs)) can ensure that onlyproperly classified partitions are allowed to be used for data trafficto remote subnets.

In accordance with an embodiment, a global management entity, such as anInter Subnet Manager (ISM) can allocate a certain P_Key range withinwhich all ISPs can reside (i.e., any ISP in such an environment musthave a P_Key within the P_Key range as defined by then ISM). By ensuringthat ISPs are allocated from a specific P_Key range, it is possible toensure that some P_Key ranges can be used for different purposes bydifferent subnets while P_Key ranges used for ISPs are used consistentlyby all relevant subnets.

In accordance with an embodiment, by observing which end-nodes aremembers of which ISPs and correlating this with what local router portsare members of the same ISPs, the set of possible inter subnet paths canbe determined both within each local subnet as well as between connectedsubnets.

In accordance with an embodiment, by observing that directly connectedrouter ports from different subnets are both members of the same set ofISPs, it can be determined that configuration is consistent in bothsubnets without exchanging additional information between the subnets.

In accordance with an embodiment, each node within a subnet can comprisecertain limitations, such as a MTU (maximum transmission unit), as wellas a maximum rate (maximum transmission rate). These limitations canvary between connected subnets, such that a node within subnet A, forexample, can comprise a smaller, bigger, or the same MTU as that setwithin connected subnet B.

In accordance with an embodiment, when a deterministic route existsbetween end-ports in different subnets, an inter-subnet control planeprotocol can exist that allows ISMs in each respective subnet to gatherpath records representing the relevant remote GIDs from any end-port inthe local subnet that shares an ISP with a corresponding remote port.

In accordance with an embodiment, in the case of directly connectedsubnets (i.e., subnets that are directly connected without anyintermediaries, such as a trivial intermediate subnet), the relevantpath information includes the LID of the intermediate local router portthat is defined by the selected route. The relevant path informationgathered by the ISMs can additionally comprise a maximum MTU and amaximum rate. In situations where the maximum MTU and maximum rate aredifferent, the ISMs can set the maximum MTU and maximum rate for theinter-subnet path record to the lower of the maximums for eachlimitation.

FIG. 19 illustrates a system for supporting an inter-subnet controlplane protocol for ensuring consistent path records, in accordance withan embodiment. More specifically, the figure shows such a control planeprotocol for two directly connected subnets.

In accordance with an embodiment, a system can comprise two or moresubnets, such as subnet A 1400 and subnet B 1410. Subnets A and B cancomprise a number of end nodes, respectively, such as end node 1401, endnode 1402, end node 1411, and end node 1412. In an effort forsimplicity, the configuration of the end nodes is not explicitly shownin the figure. One of ordinary skill in the art will understand that theend nodes can comprise a number of configurations, such as thosedescribed above in relation to physical end nodes, virtual machines,virtual switches, and the like. Subnet A can additionally comprise anumber of switches, representatively shown as switches 1404-1407, and anumber of routers, such as routers 1403 and 1408. Subnet B can likewiseadditionally comprise a number of switches, representatively shown asswitches 1414-1417, and a number of routers, such as routers 1413 and1418. It is to be understood that the routers, although shown asseparate components, can also comprise a virtual router, such as thedual-port virtual router configuration.

For example, in accordance with an embodiment, after configuration, adual-port virtual router configuration can be provided such that asubnet manager sees a proper end node, signifying an end of the subnetthat the subnet manager is responsible for. In accordance with anembodiment, at a switch 1404 in subnet A 1400, a switch port can beconnected (i.e., logically connected) to a router port in a virtualrouter 1403 via a virtual link. The virtual router 1403 (e.g., adual-port virtual router), which while shown as being external to theswitch 1404 can, in embodiments, be logically contained within theswitch 1404, can also comprise a second router port, router port II. Inaccordance with an embodiment, a physical link, which can have two ends,can connect the subnet A 1400 via first end of the physical link withsubnet B 1401 via a second end of the physical link, via router ports atthe routers in the different subnets.

In accordance with an embodiment, an end node in subnet A, such as endnode 1401, can be a member of an inter-subnet partition (ISP), such asISP A. One or more end nodes of subnet B 1410 can additionally bemembers of ISP A, thus allowing for inter-subnet data traffic between atleast the end nodes sharing a same ISP.

In accordance with an embodiment, the ISMs in the respective subnets canexchange information related to the selected path between end nodes,such as end node 1401 and end node 1412. This information can includepath information, set by each SM in their respective subnets (notshown). The path information can comprise a maximum MTU size as well asthe maximum rate.

As shown in FIG. 19, for example, within subnet A 1400, the chosen path(as shown by the dashed line) can have a MTU of a value of X, while themaximum rate can have a value of Y. Likewise, within subnet B 1410, thechosen path can have a MTU of a value of X′, while the maximum rate canhave a value of Y′.

In accordance with an embodiment, in situations where the MTU values arenot the same (X>X′ or X<X′), the ISMs can communicate 1915 to select thesmaller of the two MTU values for the chosen path. Likewise, insituations where the maximum rate values are not the same (Y>Y′ orY<Y′), the ISMs can communicate 1915 to select the smaller of the twomaximum rate values for the chosen path.

In accordance with an embodiment, in the case of directly connectedsubnets, the inter-subnet path record can take into account the maximumMTU and maximum rate allowed on the path in each of the two connectedsubnets.

In accordance with an embodiment, in the case of directly connectedsubnets, a key aspect of making sure communication restrictions thatexist in both subnets are combined so that, for instance, if there is arestriction of a maximum packet size in one subnet, and a differentmaximum packet size in a connected subnet, then the smaller of the twomaximums must be selected. This information gathered by the ISMs can becommunicated to the subnet managers in each respective subnet.

In accordance with an embodiment, by querying and retrieving the localpath information in the local subnet as well as the relevant pathinformation for the connected subnet, each ISM can construct the correctset of (maximal) path parameter values that represents the maximum rateand MTU, for the complete end-to-end path. The corresponding path recordcan then be made available via standard SA queries in each local subnet.

FIG. 20 illustrates a system for supporting an inter-subnet controlplane protocol for ensuring consistent path records, in accordance withan embodiment. More specifically, the figure shows such a control planeprotocol for two connected subnets where the connection spans anintermediate subnet.

In accordance with an embodiment, a system can comprise two or moresubnets, such as subnet A 1400 and subnet B 1410. Subnets A and B cancomprise a number of end nodes, respectively, such as end node 1401, endnode 1402, end node 1411, and end node 1412. In an effort forsimplicity, the configuration of the end nodes is not explicitly shownin the figure. One of ordinary skill in the art will understand that theend nodes can comprise a number of configurations, such as thosedescribed above in relation to physical end nodes, virtual machines,virtual switches, and the like. Subnet A can additionally comprise anumber of switches, representatively shown as switches 1404-1407, and anumber of routers, such as routers 1403 and 1408. Subnet B can likewiseadditionally comprise a number of switches, representatively shown asswitches 1414-1417, and a number of routers, such as routers 1413 and1418. It is to be understood that the routers, although shown asseparate components, can also comprise a virtual router, such as thedual-port virtual router configuration.

For example, in accordance with an embodiment, after configuration, adual-port virtual router configuration can be provided such that asubnet manager sees a proper end node, signifying an end of the subnetthat the subnet manager is responsible for. In accordance with anembodiment, at a switch 1404 in subnet A 1400, a switch port can beconnected (i.e., logically connected) to a router port in a virtualrouter 1403 via a virtual link. The virtual router 1403 (e.g., adual-port virtual router), which while shown as being external to theswitch 1404 can, in embodiments, be logically contained within theswitch 1404, can also comprise a second router port, router port II. Inaccordance with an embodiment, subnet A can be connected to subnet B viaa link that traverses an intermediate subnet 2010.

In accordance with an embodiment, an end node in subnet A, such as endnode 1401, can be a member of an inter-subnet partition (ISP), such asISP A. One or more end nodes of subnet B 1410 can additionally bemembers of ISP A, thus allowing for inter-subnet data traffic between atleast the end nodes sharing a same ISP.

In accordance with an embodiment, the ISMs in the respective subnets canexchange information related to the selected path between end nodes,such as end node 1401 and end node 1412. This information can includepath information, set by each SM in their respective subnets (notshown). The path information can comprise a maximum MTU size as well asthe maximum rate. The ISMs can also communicate 2011 and 2012,respectively, with the intermediate subnet 2010 to determine a MTU andmaximum rate allowed on the path through the intermediate subnet 2010.

As shown in FIG. 20, for example, within subnet A 1400, the chosen path(as shown by the dashed line) can have a MTU of a value of X, while themaximum rate can have a value of Y. Within subnet B 1410, the chosenpath can have a MTU of a value of X′, while the maximum rate can have avalue of Y′. Within the intermediate subnet 2010, the chosen path canhave a MTU of a value of X″, while the maximum rate can have a value ofY″.

In accordance with an embodiment, in situations where the MTU values arenot the same (e.g., X>X′>X″ or X<X′<X″), the ISMs can communicate 2015to select the smallest of the three MTU values for the chosen path.Likewise, in situations where the maximum rate values are not the same(Y>Y′ or Y<Y′), the ISMs can communicate 2015 to select the smallest ofthe two maximum rate values for the chosen path.

In accordance with an embodiment, by querying and retrieving the localpath information in the local subnet as well as the relevant pathinformation for the connected subnet as well as the intermediate subnet,each ISM can construct the correct set of (maximal) path parametervalues that represents the maximum rate and MTU, for the completeend-to-end path. The corresponding path record can then be madeavailable via standard SA queries in each local subnet.

FIG. 21 is a flow chart of a method for supporting consistent pathrecords in a high performance computing environment, in accordance withan embodiment.

At step 2110, the method can provide, at one or more computers,including one or more microprocessors, a first subnet, the first subnetcomprising a plurality of switches, the plurality of switches comprisingat least a leaf switch, wherein each of the plurality of switchescomprise a plurality of switch ports, a plurality of end nodes, whereinthe plurality of end nodes are interconnected via the plurality ofswitches; a subnet manager, the subnet manager running on one of theplurality of switches and the plurality of end nodes; and aninter-subnet manager (ISM), the inter-subnet manager running on one ofthe plurality of switches and the plurality of end nodes.

At step 2120, the method can configure a switch port of the plurality ofswitch ports as a router port.

At step 2130, the method can interconnect the first subnet with a secondsubnet via the switch port configured as a router port.

At step 2140, the method can assign an end node of the plurality of endnodes to an inter-subnet partition (ISP) of a plurality of inter-subnetpartitions.

At step 2150, the method can calculate, by the subnet manager, a firstlocal path record between the switch port configured as a router portand the end node of the plurality of end nodes assigned to the ISP,wherein the local path record comprises at least one limitation.

At step 2160, the method can communicate, by the ISM, with the secondsubnet the first local path record.

At step 2170, the method can communicate, by the ISM, with the secondsubnet the at least one limitation.

Features of the present invention can be implemented in, using, or withthe assistance of a computer program product which is a storage medium(media) or computer readable medium (media) having instructions storedthereon/in which can be used to program a processing system to performany of the features presented herein. The storage medium can include,but is not limited to, any type of disk including floppy disks, opticaldiscs, DVD, CD-ROMs, microdrive, and magneto-optical disks, ROMs, RAMs,EPROMs, EEPROMs, DRAMs, VRAMs, flash memory devices, magnetic or opticalcards, nanosystems (including molecular memory ICs), or any type ofmedia or device suitable for storing instructions and/or data.

Stored on any one of the machine readable medium (media), features ofthe present invention can be incorporated in software and/or firmwarefor controlling the hardware of a processing system, and for enabling aprocessing system to interact with other mechanism utilizing the resultsof the present invention. Such software or firmware may include, but isnot limited to, application code, device drivers, operating systems andexecution environments/containers.

Features of the invention may also be implemented in hardware using, forexample, hardware components such as application specific integratedcircuits (ASICs). Implementation of the hardware state machine so as toperform the functions described herein will be apparent to personsskilled in the relevant art.

Additionally, the present invention may be conveniently implementedusing one or more conventional general purpose or specialized digitalcomputer, computing device, machine, or microprocessor, including one ormore processors, memory and/or computer readable storage mediaprogrammed according to the teachings of the present disclosure.Appropriate software coding can readily be prepared by skilledprogrammers based on the teachings of the present disclosure, as will beapparent to those skilled in the software art.

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample, and not limitation. It will be apparent to persons skilled inthe relevant art that various changes in form and detail can be madetherein without departing from the spirit and scope of the invention.

The present invention has been described above with the aid offunctional building blocks illustrating the performance of specifiedfunctions and relationships thereof. The boundaries of these functionalbuilding blocks have often been arbitrarily defined herein for theconvenience of the description. Alternate boundaries can be defined solong as the specified functions and relationships thereof areappropriately performed. Any such alternate boundaries are thus withinthe scope and spirit of the invention.

The foregoing description of the present invention has been provided forthe purposes of illustration and description. It is not intended to beexhaustive or to limit the invention to the precise forms disclosed. Thebreadth and scope of the present invention should not be limited by anyof the above-described exemplary embodiments. Many modifications andvariations will be apparent to the practitioner skilled in the art. Themodifications and variations include any relevant combination of thedisclosed features. The embodiments were chosen and described in orderto best explain the principles of the invention and its practicalapplication, thereby enabling others skilled in the art to understandthe invention for various embodiments and with various modificationsthat are suited to the particular use contemplated. It is intended thatthe scope of the invention be defined by the following claims and theirequivalents.

What is claimed is:
 1. A system for supporting consistent path recordsin a high performance computing environment, comprising: one or moremicroprocessors; a first subnet, the first subnet comprising aninter-subnet manager (ISM) of the first subnet; a second subnet, thesecond subnet comprising an ISM of the second subnet; and wherein acommunication path is defined between an end node of the first subnetand an end node of the second subnet; wherein the communication pathcomprises a first path record defined within the first subnet, and asecond path record defined within the second subnet; wherein the firstpath record defined within the first subnet comprises a first pathparameter, the first path parameter comprising a first maximumtransmission unit (MTU) value to be enforced on packets traversing thefirst subnet along the first path record; wherein the second path recorddefined within the second subnet comprises a second path parameter, thesecond path parameter comprising a second MTU value to be enforced onpackets traversing the second subnet along the second path record, thesecond MTU value being different than the first MTU value; and whereinthe communication path comprises a third path parameter, the third pathparameter comprising the lower of the first MTU value or the second MTUvalue.
 2. The system of claim 1, further comprising: an intermediatesubnet, wherein the first and second subnets are connected via theintermediate subnet.
 3. The system of claim 2, wherein the communicationpath further comprises a third path record within the intermediatesubnet.
 4. The system of claim 3, wherein the third path recordcomprises a fourth path parameter, the fourth path parameter comprisinga third MTU value; and wherein the third path parameter comprises thelowest of the first MTU value, the second MTU value, or the third MTUvalue.
 5. The system of claim 1, wherein the first end node and thesecond end node are members of the same inter-subnet partition, theinter-subnet partition being defined by a partition key (P_Key) of aplurality of partition keys.
 6. The system of claim 5, wherein the P_Keyof the inter-subnet partition is within a range of the plurality ofP_Keys defined by both the ISM of the first subnet and the ISM of thesecond subnet as being allocated for inter-subnet data partitions. 7.The system of claim 4, wherein the first path parameter furthercomprises a first maximum transmission rate value; wherein the secondpath record further comprises a second maximum transmission rate value;wherein the fourth path parameter further comprises a third maximumtransmission rate value; and wherein the third path parameter furthercomprises the lowest of the first maximum transmission rate value, thesecond maximum transmission rate value, or the third maximumtransmission rate value.
 8. A method for supporting consistent pathrecords in a high performance computing environment, comprising:providing, at one or more computers, including one or moremicroprocessors: a first subnet, the first subnet comprising aninter-subnet manager (ISM) of the first subnet, and a second subnet, thesecond subnet comprising an ISM of the second subnet; and defining acommunication path between an end node of the first subnet and an endnode of the second subnet, the communication path comprising a firstpath record defined within the first subnet, and a second path recorddefined within the second subnet; wherein the first path record definedwithin the first subnet comprises a first path parameter, the first pathparameter comprising a first maximum transmission unit (MTU) value to beenforced on packets traversing the first subnet along the first pathrecord; wherein the second path record defined within the second subnetcomprises a second path parameter, the second path parameter comprisinga second MTU value to be enforced on packets traversing the secondsubnet along the second path record, the second MTU value beingdifferent than the first MTU value; and wherein the communication pathcomprises a third path parameter, the third path parameter comprisingthe lower of the first MTU value or the second MTU value.
 9. The methodof claim 8, further comprising: providing an intermediate subnet,wherein the first and second subnets are connected via the intermediatesubnet.
 10. The method of claim 9, wherein the communication pathfurther comprises a third path record within the intermediate subnet.11. The method of claim 10, wherein the third path record comprises afourth path parameter, the fourth path parameter comprising a third MTUvalue; and wherein the third path parameter comprises the lowest of thefirst MTU value, the second MTU value, or the third MTU value.
 12. Themethod of claim 8, wherein the first end node and the second end nodeare members of the same inter-subnet partition, the inter-subnetpartition being defined by a partition key (P_Key) of a plurality ofpartition keys.
 13. The method of claim 12, wherein the P_Key of theinter-subnet partition is within a range of the plurality of P_Keysdefined by both the ISM of the first subnet and the ISM of the secondsubnet as being allocated for inter-subnet data partitions.
 14. Themethod of claim 11, wherein the first path parameter further comprises afirst maximum transmission rate value; wherein the second path recordfurther comprises a second maximum transmission rate value; wherein thefourth path parameter further comprises a third maximum transmissionrate value; and wherein the third path parameter further comprises thelowest of the first maximum transmission rate value, the second maximumtransmission rate value, or the third maximum transmission rate value.15. A non-transitory computer readable storage medium, includinginstructions stored thereon for supporting consistent path records in ahigh performance computing environment, which when read and executed byone or more computers cause the one or more computers to perform stepscomprising: providing, at one or more computers, including one or moremicroprocessors: a first subnet, the first subnet comprising aninter-subnet manager (ISM) of the first subnet, and a second subnet, thesecond subnet comprising an ISM of the second subnet; and defining acommunication path between an end node of the first subnet and an endnode of the second subnet, the communication path comprising a firstpath record defined within the first subnet, and a second path recorddefined within the second subnet; wherein the first path record definedwithin the first subnet comprises a first path parameter, the first pathparameter comprising a first maximum transmission unit (MTU) value to beenforced on packets traversing the first subnet along the first pathrecord; wherein the second path record defined within the second subnetcomprises a second path parameter, the second path parameter comprisinga second MTU value to be enforced on packets traversing the secondsubnet along the second path record, the second MTU value beingdifferent than the first MTU value; and wherein the communication pathcomprises a third path parameter, the third path parameter comprisingthe lower of the first MTU value or the second MTU value.
 16. Thenon-transitory computer readable storage medium, of claim 15, the stepsfurther comprising: providing an intermediate subnet, wherein the firstand second subnets are connected via the intermediate subnet.
 17. Thenon-transitory computer readable storage medium, of claim 16, whereinthe communication path further comprises a third path record within theintermediate subnet.
 18. The non-transitory computer readable storagemedium, of claim 17, wherein the third path record comprises a fourthpath parameter, the fourth path parameter comprising a third MTU value;and wherein the third path parameter comprises the lowest of the firstMTU value, the second MTU value, or the third MTU value.
 19. Thenon-transitory computer readable storage medium, of claim 15, whereinthe first end node and the second end node are members of the sameinter-subnet partition, the inter-subnet partition being defined by apartition key (P_Key) of a plurality of partition keys.
 20. Thenon-transitory computer readable storage medium, of claim 19, whereinthe P_Key of the inter-subnet partition is within a range of theplurality of P_Keys defined by both the ISM of the first subnet and theISM of the second subnet as being allocated for inter-subnet datapartitions.